Rapid heater for emission control device

ABSTRACT

An emission control device having a catalyst matrix, a microwave heater and a microwave energy reflective sleeve which substantially surrounds an outer surface of the matrix is provided. In one example, power is supplied to the microwave generator only as long as the temperature of the catalyst matrix is less than the activation temperature of the emission control reactions. The microwave energy reflective sleeve may reflect and confine substantially all of a microwave energy received from a microwave generator and waveguide, improving the operability of the emission control device and reducing the light-off time of the emission control reactions.

BACKGROUND

At sufficiently elevated temperatures, catalytic emission control devices initiate surface reactions to treat exhaust gases of an engine. In one example, the catalyst surface can be heated by exposing the catalyst to hot engine exhaust gases. The surface reactions are initiated as the surface temperature rises above the activation temperature (“light-off temperature”). However, the exhaust gases passing over the catalyst prior to light-off may exit the emission control device without the desired level of treatment. It is therefore advantageous to reduce the time needed to initiate the catalytic reactions and reduce the amount of exhaust gases that are emitted with less than the desired treatment.

One approach to increase the temperature of an emission control device is to transfer energy to the devices in addition to heat transferred from hot exhaust gases. For example, a microwave energy generator may be used to promote faster catalyst heating. Microwave energy may be used to heat water molecules in the exhaust stream which then transfer heat to the catalyst surface.

SUMMARY

The above issue may be addressed by, in one example, an emission control device, which may be an emission control device comprising a can and a catalyst matrix. The matrix may have an inlet end, an outlet end, and an outer surface therebetween. The emission control device may further include a microwave energy reflective sleeve substantially surrounding at least a longitudinal portion of the outer surface, where the sleeve and the matrix are retained in the can.

For example, the microwave generator may supply microwave energy to the emission control device when the temperature of the catalyst matrix is below the light-off temperature. The microwave energy reflective sleeve surrounding the outer surface of the matrix may reduce radial microwave energy losses from the can. As such, the system may have reduced energy losses, which may thus reduce the microwave energy needed to heat the catalyst and/or reduce the time to reach the light-off temperature. Accordingly, a lower power demand and/or a faster heating time with the same supplied power may be realized.

As another example, the microwave energy supplied to the matrix may be adjusted after the emission control reactions are initiated by adjusting the operation of the microwave generator in response to a matrix temperature, an engine condition, or an exhaust gas condition. It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an internal combustion engine 10 and associated components;

FIG. 2 illustrates a perspective view of an emission control device and heating system;

FIG. 3 illustrates a side view of an emission control device;

FIG. 4 illustrates a high-level flowchart of an example operation.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram showing a multi-cylinder engine 10, which may be included in a propulsion system of an automobile. Engine 10 may be controlled at least partially by a control system including controller 12 and by input from a vehicle operator 162 via an input device 160. In this example, input device 160 includes an accelerator pedal and a pedal position sensor 164 for generating a proportional pedal position signal PP. Combustion chamber 108 may receive intake air from intake manifold 102 via intake passage 106 and may exhaust combustion gases via exhaust passage 110, and may also receive fuel injected directly into combustion chamber 108.

Intake passage 106 may include a throttle 104. In this particular example, the position of throttle 104 may be varied by controller 12 via a signal provided to an electric motor or actuator 138 communicating with throttle 104, a configuration that is commonly referred to as electronic throttle control (ETC). In this manner, throttle 104 may be operated to vary the intake air provided to combustion chamber 108 among other engine cylinders. Exhaust gas recirculation (EGR) loop 112 may receive exhaust gases from exhaust passage 110 upstream of emission control device 120. EGR loop 112 is shown coupled to EGR valve 114, which may be adjusted by controller 12 via actuator 136. In this way, EGR valve 114 may be operated to vary the ratio of recirculated exhaust gases to the fresh air received from intake manifold 102.

Exhaust gas sensor 130 is shown coupled to exhaust passage 110 upstream of emission control device 120. Sensor 130 may cooperate with sensor 132, which is shown coupled to tailpipe 116 downstream of emission control device 120. In some examples, sensors 130 or 132 may provide an indication of exhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or CO sensor. In other examples, sensors 130 or 132 may measure the water concentration of the exhaust stream.

FIG. 1 also illustrates an emission control device 120, which is arranged along exhaust passage 110 downstream of exhaust gas sensor 130 and upstream of tailpipe 116. In one example, emission control device 120 may be a catalytic converter. FIG. 1 further depicts emission control system 144, which is shown to include at least microwave system 142 and emission control device 120.

Emission control device 120 may be a three-way catalyst (TWC), NOx trap, various other emission control devices, or combinations thereof. In some embodiments, during operation of engine 10, emission control device 120 may be periodically reset by operating at least one cylinder of the engine within a particular air/fuel ratio. In this embodiment, emission control device 120 is also configured to include temperature sensor 140, which may be configured to measure the temperature of the exhaust gas stream or of matrix 230 (see FIG. 2) to facilitate characterization of the catalyst matrix by controller 12.

The microwave system 142 depicted in FIG. 1 includes the microwave generator 122 and waveguide 124. The waveguide 124 is shown coupled between generator 122 and emission control device 120. Microwave generator 122 is shown in electrical communication with generator controller 128. Generator controller 128 is in electrical communication with input/output ports 152 of controller 12, such that controller 12 may adjust the operation of microwave generator 122. In some embodiments, controller 12 communicates with microwave generator controller 128 to adjust the operation of microwave generator 122 responsive to measurements made by temperature sensor 140 or by sensors 130 and 132. In other examples, controller 12 may include the microwave generator controller.

Controller 12 is shown in FIG. 1 as a microcomputer, including microprocessor unit 150, input/output ports 152, an electronic storage medium for executable programs and calibration values shown as read-only memory chip 154 in this particular example, random access memory 156, keep alive memory 158, and a data bus. Controller 12 may receive various signals from sensors coupled to engine 10, in addition to those signals previously discussed, including measurement of inducted mass air flow (MAF); engine coolant temperature (ECT); a profile ignition pickup signal; throttle position (TP) from a throttle position sensor; and absolute manifold pressure signal, MAP. Engine speed signal, RPM, may be generated by controller 12. Manifold pressure signal MAP from a manifold pressure sensor may be used to provide an indication of vacuum, or pressure, in the intake manifold. Storage medium read-only memory 154 can be programmed with computer readable data representing instructions executable by processor 150 for performing the methods described below as well as other variants that are anticipated but not specifically listed.

FIG. 2 illustrates an example of the emission control system 144 introduced in FIG. 1. Microwave generator 122 is shown connected to emission control device 120 via waveguide 124, such that microwave energy produced by the generator is transferred to the emission control device.

Emission control device 120, shown in a cutaway perspective, is configured to receive exhaust gas from exhaust passage 110 (FIG. 1) and supply treated exhaust gas to tailpipe 116 (FIG. 1). Additional emission control devices, catalyst, and/or mufflers may also be provided in the exhaust passage. A primary axis A and a secondary axis B associated with emission control device 120 are illustrated in FIG. 2. In this example, axis A is depicted substantially parallel to the direction of exhaust gas flow F, while axis B is oriented perpendicular to axis A. Specifically in this example, in which emission control device 120 is substantially cylindrical, A is illustrated as a longitudinal axis, and B is shown as a radial axis.

The microwave generator 122 produces microwave energy that is routed to the emission control device to increase the temperature of the device. In one example, microwave generator 122 is a solid-state power oscillator producing microwave energy in the range of 2.4-2.5 GHz. Waveguide 124 transfers the microwave energy from generator 122 to emission control device 120. In this example, waveguide 124 is illustrated as a hollow conductor, which may be fabricated from metal in some examples. As depicted here, waveguide 124 includes plug 126, which is shown adjacent an interface configured to be coupled to can 210. In some embodiments, plug 126 may be configured to keep gases (water vapor, in one example) from entering waveguide 124 by forming a hermetic seal with can 210. Plug 126 is fabricated from fused quartz in some examples, which may have a low coefficient of thermal expansion to moderate internal stresses within a design tolerance during thermal cycling of emission control device 120, but it is recognized that the materials of construction for waveguide 124 and plug 126 may vary depending on the application. For example, plug 126 may be fabricated from a dielectric material, including inorganic materials such as silicon nitride. Plug 126 may also be configured to include a sensor feedthrough (not shown). For example, temperature sensor 140 may be located at plug 126 to measure the temperature of matrix 230.

Microwave energy produced by generator 122 and transmitted via waveguide 124 is received by emission control device 120. As shown in FIG. 2, emission control device 120 includes can 210, microwave energy reflective mesh end walls 220, catalyst matrix 230, and microwave energy reflective sleeve 240.

In this example, can 210 is illustrated as a substantially cylindrical casing, which may be made of metal. Can 210 may be configured to provide structural support and protection for emission control device 120 in addition to retaining matrix 230 and sleeve 240 within the exhaust system. Can 210 may include silencers, thermal shields, etc. not illustrated in FIG. 2, as well as feedthroughs for sensors, temperature gauges, or sampling ports.

Retained within can 210 is catalyst matrix 230. As illustrated in FIG. 2, matrix 230 includes an inlet end 200 and an outlet end 202. Exhaust gas flow F crosses inlet end 200 as it enters matrix 230. The gases flow through the catalyst, exiting matrix 230 at outlet end 202. FIG. 2 illustrates matrix 230 with a honeycomb-structured monolith, but it is understood that other shapes may be employed. For example, matrix 230 may include a packed bed or one or more porous membranes. Matrix 230 may include a metal or ceramic support structure and the surface of matrix 230 may be impregnated with catalyst particles in a variety of ways, such as a washcoat or physical vapor deposition, etc. The catalyst particles may include species active in the reduction and oxidation of exhaust gases; for example, the catalyst particles may include palladium, platinum, rhodium, or other metals, metal oxides, or a combination thereof depending on the catalytic application.

Substantially surrounding the outer surface 235 of matrix 230 is the microwave energy reflective sleeve 240. Reflective sleeve 240 reflects and confines incident microwave energy; for example, microwave energy traveling in the direction of axis B would be reflected by sleeve 240. Reflective sleeve 240 may be formed from a conductive material, and may include an opening or an area of microwave transparent material configured to receive microwave energy from waveguide 124 and transmit it to matrix 230. In some examples, reflective sleeve 240 is a mesh with openings configured to be smaller than the wavelength of the incident microwave energy so that the energy is reflected by the mesh. Reflective sleeve 240 may also be fabricated from a material configured to protect matrix 230. For example, reflective sleeve 240 may be flexible and shock-resistant to cushion matrix 230 against can 210. In other examples, a separate sleeve of protective material (not shown) may be located between reflective sleeve 240 and can 210, to further protect, support, and retain at least matrix 230 and reflective sleeve 240.

FIG. 3 shows a side view of another example of emission control device 120. In this example, the reflective sleeve 240 is shown covering only a portion of matrix 230 near the inlet end 200. Microwave energy from generator 122 (not shown) is communicated via the waveguide 124 and is received by emission control device 120. In the interests of clarity, plug 126 is shown intruding slightly below reflective sleeve 240, but it should be understood that this is a non-limiting example, and that other configurations may be employed. As depicted, reflective sleeve 240 reflects and confines a radial distribution of microwave energy near inlet end 200. For example, by only providing microwave energy to the matrix 230 near the inlet end, and allowing the heat generated by the emission control reactions at that portion of the matrix to supply heat to the portion of matrix 230 downstream, a reduction in overall microwave energy supplied to emission control device 120 may be possible. However, it is recognized that in other embodiments it may be beneficial to reflect and confine the microwave energy received by emission control device 120 to substantially the entire volume of matrix 230. For example, it may be possible to reduce the heating time of matrix 230, to reduce microwave losses and improve control of emission control system 144, etc., if the emission control device 120 is so configured.

Thus, in some embodiments it may be desirable to provide additional microwave energy confinement and reflection. Returning to FIG. 2, an example of the emission control device 120, which may include microwave energy reflective mesh end walls 220 located at inlet 200 and outlet 202 is shown. In this example, mesh end walls 220 reflect and confine microwave energy distributed along axis A while allowing exhaust gas flow F to pass into and out of matrix 230. Accordingly, the combination of mesh end walls 220 and reflective sleeve 240 depicted in FIG. 2 substantially confines the microwave energy to the volume occupied by matrix 230. However, in other examples mesh end walls 220 may not be included. For example, microwave energy distributed along axis A may be reflected by baffles or other microwave reflective features which may be present near inlet end 200 or outlet end 202 of matrix 230. In such an example, the microwave energy received by emission control device 120 may also be substantially confined to the volume occupied by matrix 230. In another example, the end walls 200 and sleeve 240 may form a unitary structure.

By radially confining and reflecting the microwave energy received by emission control device to the volume occupied by the catalyst, via sleeve 240, it is possible to improve catalyst operability by heating the surface of the matrix.

For example, controller 12 may be configured to adjust the microwave energy output of microwave generator 122 responsive to a temperature of matrix 230. Under cold start conditions, where the temperature of the catalyst is below an activation temperature of an active catalyst particle on the surface of matrix 230, microwave energy produced by generator 122 is supplied to emission control device 120. In this example, the microwave energy received by emission control device 120 is confined radially by reflective sleeve 240, and longitudinally by mesh end walls 220. Exhaust gases containing water are exposed to the confined microwave energy. Water vapor heated by the microwave energy transfers heat to the catalyst surface.

According to some embodiments, once the catalyst becomes warm enough (in this example, as measured by temperature sensor 140) to initiate the emission control reactions, the output of microwave generator 122 is reduced or terminated. Specifically, the duration of microwave generation may be on the order of 30 to 60 seconds to achieve light-off; after the reactions are initiated, microwave generator 122 may be turned off to conserve power or reduce the load on an automobile electrical system.

In yet another example, a microwave-heated device having a microwave energy reflective sleeve to address radially-emitted radiation may be lead to a better characterization of microwave energy losses. As such, the use of a microwave energy reflective sleeve surrounding at least a portion of the outer surface of the catalyst matrix may reduce the influence of those losses and may permit a more robust control routine for the emission control device. Still further operations of the control system are described below with regard to FIG. 4.

FIG. 4 illustrates an exemplary routine 400 for controlling the microwave energy supplied by microwave generator 122 according to one example. In this example, the temperature of the matrix 230 is measured at 410 by temperature sensor 140. However, in alternative examples, the temperature may be estimated based on engine operating conditions, ambient conditions, etc.

At 420, the matrix temperature is compared to the light-off temperature of the catalyst. If the temperature is above the light-off temperature, the routine proceeds to 460 where microwave generator 122 is turned off and the routine ends. Alternatively, if the temperature is below the activation temperature, the routine proceeds to 425 and checks the power state of the generator. If the generator is turned off, the routine proceeds to 430 and turns the generator on, supplying microwave energy to emission control device 120. If the generator is on at 425, the routine skips to 440. At 440, an exhaust gas condition is measured. The microwave energy output of microwave generator 122 is then adjusted responsive to the condition of the exhaust gas at 450. Control then passes back to 410, wherein the routine continues.

It is understood that the operation of generator 122 may be adjusted by controller 12 according to other conditions of the engine in other embodiments. For example, the microwave generator operation may be adjusted in response to an exhaust gas recirculation ratio, an engine speed, a spark timing, a fuel injection amount, or a driver tip-in. These conditions may affect the temperature of the exhaust stream exiting the engine, and may change the operating temperature of emission control device 120. In this way, the amount of microwave energy provided may be coordinated with engine, exhaust, and catalyst operating conditions.

Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various acts, operations, or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated acts or functions may be repeatedly performed depending on the particular strategy being used. Further, the described acts may graphically represent code to be programmed into the computer readable storage medium in the engine control system.

It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure. 

1. An emission control device, comprising: a can; a matrix, the matrix having an inlet end, an outlet end, and an outer surface therebetween; a microwave energy reflective sleeve substantially surrounding the outer surface, where the sleeve and matrix are retained in the can.
 2. The emission control device of claim 1, wherein the matrix further comprises a washcoated monolith.
 3. The emission control device of claim 2, wherein a microwave energy reflective mesh end wall is adjacent to each of the inlet end and the outlet end of the matrix.
 4. The emission control device of claim 1, wherein the can further comprises an interface configured to be coupled to a waveguide.
 5. The emission control device of claim 1, wherein the sleeve further comprises a flexible and shock-resistant material configured to protect the matrix.
 6. An emission control system for a vehicle, comprising: a microwave generator; a waveguide configured to receive microwave energy from the microwave generator; and an emission control device configured to receive microwave energy from the waveguide, the emission control device further comprising: a can; a matrix having an inlet and an outlet; a microwave energy reflective sleeve substantially surrounding the matrix, wherein the sleeve and matrix are retained in the can; and at least two microwave energy reflecting mesh end walls respectively coupled to the inlet and outlet of the matrix.
 7. The emission control system of claim 6, further comprising a controller configured to adjust microwave energy output of the microwave generator responsive to an exhaust condition of an exhaust stream from an internal combustion engine.
 8. The emission control system of claim 7, further comprising a controller configured to adjust microwave energy output of the microwave generator responsive to a temperature of the matrix.
 9. The emission control system of claim 8, wherein the microwave generator supplies microwave energy to the emission control device when the temperature of the matrix is below an activation temperature of an active catalyst particle on a surface of the matrix.
 10. The emission control system of claim 6, wherein the matrix is a catalytically active monolith.
 11. The emission control system of claim 6, the waveguide further comprising a fused quartz plug adjacent an interface configured to be coupled to the can.
 12. An emission control system for treating exhaust gasses of an internal combustion engine, comprising: a microwave system comprising at least: a microwave energy generator, and a waveguide configured to receive microwave energy from the generator, an emission control device coupled to the microwave heater, the emission control device including a can; a matrix, the matrix having an inlet end, and outlet end, and an outer surface therebetween; and a microwave energy reflective sleeve substantially surrounding the outer surface, where the mesh and matrix are retained in the can; and a controller configured to adjust the microwave energy generator responsive to a condition of the exhaust gasses from the internal combustion engine.
 13. The emission control system of claim 12, wherein the controller is further configured to adjust the generator responsive to an exhaust condition, wherein the controller is further configured to operate the generator at a frequency of 2.45±0.20 GHz.
 14. The emission control system of claim 12, wherein the matrix further comprises a washcoated monolith, wherein a microwave energy reflective mesh end wall is adjacent to each of the inlet end and the outlet end of the matrix, and wherein the can further comprises an interface configured to be coupled to the waveguide.
 15. The emission control system of claim 12, wherein the sleeve further comprises a flexible and shock-resistant material configured to protect the matrix.
 16. The emission control system of claim 12, wherein the controller is further configured to adjust microwave energy output of the microwave generator responsive to a temperature of the matrix.
 17. The emission control system of claim 12, wherein the controller is further configured to adjust the operation of the generator responsive to a condition of an internal combustion engine.
 18. The emission control system of claim 17, wherein the condition of the internal combustion engine includes one or more of an exhaust gas recirculation ratio, an engine speed, a spark timing, a fuel injection amount, or a driver tip-in.
 19. The emission control system of claim 12, wherein the waveguide further comprises a fused quartz plug adjacent the circumferential surface of the emission control device.
 20. The emission control system of claim 19, wherein the sleeve further comprises a microwave energy reflective mesh. 